Minutes of 12th FFIR meeting on 6/21/2000

The meeting was held in a room of 3-425 at KEK, 13:30-14:30, 6/21/2000. We discussed on (1) dump line update and others.

(1) Dump line update: (transparencies, 4 pages of pdf,27.7kB) or tiff, 161kB Kubo calculated neutron backgrounds at the updated dump line taking account of QC1&QC2 magnetic fields along the beam line. For the calculations, he set following apertures of major optical elements on the line;

QC1 entrance   -0.01 < x < 0.1    -0.01 < y < 0.01
QC2 exit       -0.02 < x < 0.1    -0.01 < y < 0.01
QC2 entrance   -0.02 < x < 0.1    -0.01 < y < 0.01
QC2 exit       -0.08 < x < 0.1    -0.01 < y < 0.01
from QC2    -s*0.006 < x < 0.1    -0.01 < y < 0.01
BV1,BV2        -0.02 < x < 0.02   -0.05 < y < 0.05
,where unit is meter(m) and x,y are measured from the extracted beam axis. Vertical bending magnet (BV1) is located at about 65m from IP. The major difference from previous settings is asymmetric apertures both in horizontal and vertical directions, while the apertures have not been optimized.

New results show much less beam loss than the previous ones by about 1/100. The major loss occurs at the BV1 and BV2 where horizontal appertures are the smallest. Assuming 1 neutron/100 MeV energy deposit, neutrons yield 10^12/cm^2/10^7sec without any shield between loss points and IP, which exceeds the tolerable level of 10^10/cm^2/10^7sec. We could reduce the losses at the BV1&2 by using dipole magnets of septum-type.

Anyway, we were very encouraged to see the significant reduction of beam losses by the asymmetric apertures since it seems to be not so difficult to obtain further reduction of 10^3-10^4 by proper shields.

(4) Others At next meeting, we will discuss on the prototype of support tube, superconducting final focus magnets and new FF optics design etc. .

The next meeting will be on 19 July, 2000 13:30 - 15:30 at 3 gokan, 425.